Magnetic Effects of Electric Current Class 10 Notes and Questions

What Magnetic Effects of Electric Current is about

Weightage: This chapter is part of Unit IV, Effects of Current, which carries 13 of the 80 theory marks together with Electricity.Source: CBSE Science syllabus 2026-27, Unit IV Effects of Current

In real board papers: asked in 21 of the 21 board papers we hold (2023 to 2026), on average 5.1 marks per paper. See the questions

Key concepts

Magnetic Field and Field Lines

NCERT section 12.1 Magnetic Field and Field Lines

A compass needle is just a tiny bar magnet. Its end that points roughly north is the north pole; the other end is the south pole. Like poles repel and unlike poles attract, which is why a magnet brought near a compass makes the needle turn.

The region around a magnet where its force can be felt is its magnetic field. A field has both size and direction. Its direction at a point is the way a north pole would move if placed there.

We picture the field with field lines, the path a free north pole would tend to follow. Iron filings (Activity 12.2) or a compass moved step by step (Activity 12.3) trace them.

• Outside the magnet, lines run from north pole to south pole; inside, from south to north. So every line is a closed curve.
• Where lines are crowded, the field is stronger. That is why the compass deflects more near the poles.
• Two lines never cross: at a crossing the compass would have to point two ways at once, which is impossible.

Worked example

A student plots the field lines of a bar magnet using a small compass, as in Activity 12.3.

(a) Why does she move the compass each time so that its south end sits exactly where its north end was before?
(b) Near which part of the magnet does the needle deflect the most, and what does this tell you about the field there?
(c) Give the reason why two of her field lines can never cross. (3 marks)

Try it first, then show the solutionSolution

1. (a) The north end of the needle shows the field direction at that point. Moving the compass forward each time traces the path a north pole would follow, giving one continuous line from the N pole to the S pole. (1 mark)
2. (b) The deflection is greatest near the poles, where the lines are crowded together, so the field is strongest there. (1 mark)
3. (c) At a crossing point the field would have two directions, so the compass needle would have to point two ways at once, which is impossible. (1 mark)

Answer: (a) To follow the field direction step by step and get one continuous field line. (b) Near the poles; the field is strongest where the lines are crowded. (c) A crossing would mean two field directions at one point, which a compass cannot show.

Magnetic Field due to a Straight Current-Carrying Conductor

NCERT section 12.2.1 Magnetic Field due to a Current through a Straight Conductor

In Activity 12.1 a compass near a thick copper wire deflects only when the key is closed. So the current itself creates a magnetic field.

Activity 12.4 shows that the direction of this field depends on the direction of current. With current from north to south in a wire held over the compass, the north pole of the needle moves east. Reverse the cell connections so current flows south to north, and the needle moves west. Reversing the current reverses the field.

Activity 12.5 passes a vertical wire through a horizontal cardboard. Iron filings on the card form concentric circles centred on the wire. These circles are the field lines.

Two results matter for exams:

• At a fixed point, more current gives more deflection, so the field grows as the current grows.
• With the same current, a compass placed farther away deflects less, so the field weakens with distance. The circles get larger and larger, and more spread out, as you move outwards.

The pattern of a field depends on the shape of the conductor, which is why the loop and solenoid come next.

Worked example

In Activity 12.5, a student places a compass at point P, 2 cm from a vertical copper wire, and notes the deflection when the current is 1 A. Predict, with a reason, what happens to the deflection if:

(i) the current is raised to 2 A with the compass still at P;
(ii) the current is kept at 1 A but the compass is moved to point Q, 6 cm from the wire;
(iii) the battery connections are reversed. (3 marks)

Try it first, then show the solutionSolution

1. (i) The deflection increases, because the magnetic field at a given point increases when the current increases. (1 mark)
2. (ii) The deflection decreases, because for the same current the field becomes weaker as the distance from the wire increases. (1 mark)
3. (iii) The needle deflects the opposite way, because reversing the current reverses the direction of the magnetic field. (1 mark)

Answer: (i) Deflection increases. (ii) Deflection decreases. (iii) Needle deflects in the opposite direction.

Right-Hand Thumb Rule

NCERT section 12.2.2 Right-Hand Thumb Rule

You need a quick way to find which way the circular field lines around a straight wire go. That is the right-hand thumb rule.

Imagine holding the wire in your right hand with your thumb pointing along the current. Your curled fingers then show the direction of the field lines around the wire. The NCERT text also calls this Maxwell's corkscrew rule: if you drive a corkscrew along the current, its turning shows the field direction.

Why it works so neatly: the field lines around a straight wire are circles, and your curled fingers also make a circle around the wire. The rule just tells you clockwise or anticlockwise.

How to use it in exams:

• Fix the current direction first (thumb).
• Decide where you are viewing from. Current coming towards you gives anticlockwise field lines; current going away from you gives clockwise lines.
• At any point, the field is along the tangent to the circle, and a compass north pole there points along that tangent.

The same rule, applied to each bit of a curved wire, gives the field of a loop and a solenoid.

Worked example

A straight wire passes vertically through the centre of a horizontal cardboard sheet and carries current vertically upwards.

(a) Seen from above, are the magnetic field lines on the cardboard clockwise or anticlockwise?
(b) A compass is placed on the cardboard due east of the wire. In which direction will its north pole point? (2 marks)

Try it first, then show the solutionSolution

1. (a) Point the right thumb upwards along the current; the fingers curl anticlockwise when seen from above, so the field lines are anticlockwise. (1 mark)
2. (b) On an anticlockwise circle seen from above, the tangent at the point due east of the centre points towards the north, so the compass north pole points north. (1 mark)

Answer: (a) Anticlockwise, seen from above. (b) Towards the north.

Magnetic Field due to a Circular Loop

NCERT section 12.2.3 Magnetic Field due to a Current through a Circular Loop

Now bend the straight wire into a circle. Every small part of the loop still makes its own circular field lines around it. Close to the wire these circles are small; as you move towards the centre of the loop they grow so large that their arcs look like straight lines at the centre.

Apply the right-hand thumb rule to each part of the loop and you find that every part sends its field in the same direction inside the loop. So the contributions add up instead of cancelling.

Outside the loop the field points the opposite way to the field inside, because the lines come round in closed paths.

Now take a coil of n turns. Each turn carries the same current in the same sense, so the field of each turn adds up. The field of the coil is n times the field of one turn. Activity 12.6 shows this pattern with iron filings around a coil passing through a cardboard.

A quick link: current that looks anticlockwise to you makes the field inside point towards you; clockwise current makes it point away from you.

Worked example

A circular coil of 50 turns lies flat on a table. The current in it flows anticlockwise when seen from above.

(a) What is the direction of the magnetic field inside the coil and outside the coil?
(b) How does the field at the centre compare with that of a single turn carrying the same current? Give the reason. (3 marks)

Try it first, then show the solutionSolution

1. (a) Applying the right-hand thumb rule to any part of the coil, the fingers inside the loop point upwards, so the field inside is vertically upwards, out of the table. (1 mark)
2. Outside the coil the field lines return in the opposite sense, so the field outside is vertically downwards, into the table. (1 mark)
3. (b) The field is 50 times that of one turn (½ mark), because each turn carries current in the same direction, so the fields of all turns add up. (½ mark)

Answer: (a) Inside: vertically upwards (out of the table); outside: vertically downwards (into the table). (b) 50 times stronger, since the fields of all 50 turns add up.

Solenoid and Electromagnet

NCERT section 12.2.4 Magnetic Field due to a Current in a Solenoid

A solenoid is a coil of many circular turns of insulated copper wire wound closely in the shape of a cylinder. It is like many circular loops placed side by side, so their fields add up along the axis.

Its field pattern looks just like that of a bar magnet: one end acts as a north pole and the other as a south pole. Inside, the field lines are parallel straight lines, which means the field is the same at every point inside. A uniform field inside is the key fact examiners test.

To name the poles, look at one end. If the current there appears anticlockwise, the field inside points towards you, lines come out of that end, so it is a north pole. Clockwise means a south pole.

The strong field inside can magnetise a piece of magnetic material such as soft iron placed in the coil. This gives an electromagnet: a soft iron core wrapped with a coil of insulated copper wire. Because the field is made by the current, you can make it stronger by using more turns or a larger current.

Worked example

A solenoid is connected to a battery. When you look at end A, the current in the turns appears to flow clockwise.

(a) Is end A a north pole or a south pole? Give the reason.
(b) What is placed inside the solenoid to make an electromagnet, and why does it become a magnet?
(c) State two ways to make this electromagnet stronger. (3 marks)

Try it first, then show the solutionSolution

1. (a) End A is a south pole. (½ mark)
2. Clockwise current seen from A makes the field inside point away from you (right-hand thumb rule), so the field lines enter at A, and lines enter a magnet at its south pole. (½ mark)
3. (b) A soft iron core is placed inside. (½ mark)
4. The strong magnetic field inside the current-carrying solenoid magnetises it. (½ mark)
5. (c) Increase the number of turns in the coil. (½ mark)
6. Increase the current through the coil. (½ mark)

Answer: (a) South pole. (b) A soft iron core, magnetised by the strong field inside the solenoid. (c) More turns; more current.

Force on a Current-Carrying Conductor and Fleming's Left-Hand Rule

NCERT section 12.3 Force on a Current-Carrying Conductor in a Magnetic Field

A current makes a field that pushes a nearby magnet. Ampere suggested that the magnet must push back on the wire with an equal and opposite force. Activity 12.7 shows this: a small aluminium rod hung between the poles of a horse-shoe magnet moves sideways when current flows through it.

What the activity shows:

• Reverse the current and the rod moves the other way.
• Reverse the field (swap the magnet's poles) and the force again reverses.
• So the force depends on both directions. Reverse both together and the force stays the same.
• The force is largest when the current is at right angles to the field.

In that perpendicular case the force is at right angles to both. Fleming's left-hand rule gives its direction: stretch the thumb, forefinger and middle finger of your left hand so they are mutually perpendicular. Forefinger along the field, middle finger along the current, and the thumb gives the force (motion).

For a moving electron, take the current opposite to its motion before using the rule. Loudspeakers, microphones and measuring instruments use this force.

Worked example

A beam of electrons moves horizontally towards the east through a region where the magnetic field acts vertically downwards. The beam is deflected towards the:
(a) north
(b) south
(c) vertically upward direction
(d) west
(1 mark)

Try it first, then show the solutionSolution

1. Current is taken opposite to the motion of electrons, so the current is towards the west.
2. Using Fleming's left-hand rule: forefinger pointing vertically downwards (field), middle finger pointing west (current); the thumb then points towards the south.
3. The force is perpendicular to both field and current, so it lies horizontally, towards the south. (1 mark)

Answer: Option (b): towards the south.

Direct Current and Alternating Current

NCERT section 12.4 Domestic Electric Circuits

The cells and batteries used in this chapter's activities give direct current (DC): current that flows in one direction only. In Activity 12.4 the current reversed only because you changed the cell connections by hand.

The supply in your home is different. NCERT states that we receive AC (alternating current) at 220 V with a frequency of 50 Hz. Alternating current reverses its direction again and again at regular intervals.

Frequency is the number of complete cycles in one second. In one cycle the current flows one way and then the other way, so it changes direction twice per cycle. At 50 Hz there are 50 cycles per second, so the current changes direction 100 times every second, that is, once every $\frac{1}{100}$ s.

The syllabus also asks for the advantage of AC over DC. As given in the CBSE Reading Material: electric power in the form of AC can be sent over long distances without much loss of energy. How AC is produced (the generator) is not in the board exam, so do not write about it.

Worked example

(a) Name the type of current given by the cells used in Activity 12.4 and state how it differs from the current supplied to your home.
(b) Domestic supply in India is AC at 220 V, 50 Hz. What does 50 Hz mean? How many times does the current change direction in one second?
(c) State one advantage of AC over DC. (3 marks)

Try it first, then show the solutionSolution

1. (a) Cells give direct current, which flows in one direction only, whereas the home supply is alternating current, which keeps reversing its direction. (1 mark)
2. (b) 50 Hz means the current completes 50 cycles in one second. (½ mark)
3. Each cycle has two changes of direction, so the current changes direction 2 × 50 = 100 times in one second. (½ mark)
4. (c) AC can be transmitted over long distances without much loss of energy. (1 mark)

Answer: (a) Direct current, one direction only; home supply is AC. (b) 50 cycles per second; 100 changes of direction per second. (c) AC can be sent over long distances without much loss of energy.

Domestic Electric Circuits: Wiring and Parallel Connection

NCERT section 12.4 Domestic Electric Circuits

Electricity reaches a house through the mains, either by overhead poles or underground cables. Two wires matter first:

• Live wire, usually red insulation.
• Neutral wire, usually black insulation.
• The potential difference between them is 220 V.

At the meter-board these wires pass through a main fuse into the electricity meter, then through the main switch to the line wires of the house. The house is usually split into two circuits: a 15 A circuit for high-power appliances such as geysers and air coolers, and a 5 A circuit for bulbs, fans and similar.

All appliances are connected in parallel across the live and neutral wires, each with its own ON/OFF switch. Why parallel? Every appliance then gets the same 220 V, and each can be switched on or off without affecting the others.

To decide which circuit an appliance needs, find its current using $P=VI$ from the Electricity chapter, so $I=\frac{P}{V}$. If the current is more than 5 A, it needs the 15 A circuit.

Worked example

A house has a 5 A circuit and a 15 A circuit, both at 220 V.

(i) Which circuit should a 2200 W geyser be connected to? Show your working.
(ii) Which circuit is enough for a 110 W fan? Show your working.
(iii) Give two reasons why appliances in a house are connected in parallel and not in series. (3 marks)

Try it first, then show the solutionSolution

1. (i) $I=\frac{P}{V}=\frac{2200\text{ W}}{220\text{ V}}=10\text{ A}$; this is more than 5 A, so the geyser must go on the 15 A circuit. (1 mark)
2. (ii) $I=\frac{110\text{ W}}{220\text{ V}}=0.5\text{ A}$; this is well within 5 A, so the 5 A circuit is enough. (1 mark)
3. (iii) In parallel, each appliance gets the same potential difference of 220 V (½ mark), and each has its own switch, so it can be turned on or off independently. (½ mark)

Answer: (i) 10 A, so the 15 A circuit. (ii) 0.5 A, so the 5 A circuit. (iii) Each gets the full 220 V and can be switched independently.

Safety in Domestic Circuits: Earthing, Fuse, Short-Circuit and Overloading

NCERT section 12.4 Domestic Electric Circuits

Earth wire. The third wire has green insulation and is connected to a metal plate buried deep in the ground near the house. The metal body of an appliance such as an electric press, toaster, table fan or refrigerator is joined to it. If current leaks onto the body, the earth wire gives it a low-resistance path, keeping the body at the potential of the earth, so the user does not get a severe shock.

Short-circuit. When damaged insulation or a fault in an appliance lets the live and neutral wires touch directly, the current suddenly becomes very large.

Overloading. Too much current can also flow because of an accidental rise in the supply voltage or too many appliances on one socket.

Fuse. The fuse is the most important safety device. When the current becomes unduly high, Joule heating melts the fuse wire, which breaks the circuit and protects the wiring and appliances.

So short-circuiting is one cause of overloading; the fuse protects against both, while the earth wire protects the person.

Worked example

A room is on a 5 A circuit at 220 V. A 660 W heater and a 440 W electric iron are both switched on.

(a) Calculate the total current drawn.
(b) A 220 W appliance is now also switched on from the same socket. Find the new current. What does the fuse do, and why?
(c) How is this situation different from a short-circuit?
(d) Why must the iron's metal body be connected to the earth wire? (5 marks)

Try it first, then show the solutionSolution

1. (a) Total power $=660+440=1100\text{ W}$; $I=\frac{1100\text{ W}}{220\text{ V}}=5\text{ A}$. (1 mark)
2. (b) New power $=1100+220=1320\text{ W}$; $I=\frac{1320\text{ W}}{220\text{ V}}=6\text{ A}$. (1 mark)
3. This is above the 5 A rating, so the circuit is overloaded; Joule heating melts the fuse wire, which breaks the circuit and stops the high current. (1 mark)
4. (c) Here overloading is caused by too many appliances on one socket; a short-circuit happens when the live and neutral wires touch directly (damaged insulation or a faulty appliance) and the current rises abruptly. (1 mark)
5. (d) The earth wire gives leaked current a low-resistance path and keeps the metal body at earth's potential, so the user does not get a severe shock. (1 mark)

Answer: (a) 5 A. (b) 6 A; the fuse melts and breaks the circuit because the current exceeds 5 A. (c) Overloading from too many appliances, not live touching neutral. (d) To give leakage current a low-resistance path to earth and prevent a severe shock.

Science in real life: Magnetic Effects of Electric Current

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Topics in this chapter

• Magnetic Field and Field LinesComing soon
• Magnetic Field due to Current in a Straight ConductorComing soon
• Magnetic Field due to Circular Loop and Solenoid
• Force on a Current-Carrying Conductor and Fleming's Left-Hand Rule
• Direct and Alternating CurrentComing soon
• Domestic Electric Circuits
• Electric Motor, Electromagnetic Induction and Generator

Magnetic Effects of Electric Current: formulas and key facts

Direction of magnetic field lines

Outside a magnet: N pole $\to$ S pole; inside: S pole $\to$ N pole, so lines are closed curves

Use for MCQs and AR items on bar magnets and for drawing arrows on field-line diagrams.

Properties of field lines

• •Lines never cross
• •crowded lines mean a stronger field
• •field direction at a point is the way a north pole would move

The standard 'list the properties' and 'why can't two lines intersect' answers.

Field near a straight wire

Field grows with current ($B\propto I$) and weakens with distance ($B\propto \frac{1}{r}$); lines are concentric circles centred on the wire

Use for predicting compass deflection when current or distance changes.

Coil of n turns

$B_{\text{coil}}=n\times B_{\text{one turn}}$

Same current in every turn, so fields add. Explains why more turns make a stronger coil or electromagnet.

Right-hand thumb rule

Right thumb along current; curled fingers show the field direction

For straight wires, loops and solenoid poles. Never use the left hand here.

Solenoid

Field inside is uniform (parallel straight lines); end with anticlockwise current seen from outside is N, clockwise is S

Use to name poles and to answer 'field inside a solenoid is...' MCQs (same at all points).

Electromagnet

Soft iron core + coil of insulated copper wire; stronger with more turns or more current

For 'how is an electromagnet made' and 'two ways to increase its strength'.

Fleming's left-hand rule

$Forefinger=field,middlefinger=current,thumb=force(motion),allmutuallyperpendicular$

Use only when current and field are at right angles. Force is largest in this case.

Reversal rule for force

Reverse current OR field: force reverses; reverse BOTH: force unchanged

Check how many quantities you reverse in an assertion-reason item: one reversal flips the force, two cancel.

Current for a moving charge

$Electronmovingoneway=currentintheoppositedirection;protonoralphaparticle=currentalongitsmotion$

Convert to current direction before applying Fleming's rule.

Current drawn by an appliance

$P=VI\Rightarrow I=\frac{P}{V}$

From the Electricity chapter. Use to decide 5 A or 15 A circuit and to check overloading.

Domestic supply

AC at $220\text{ V}$, frequency $50\text{ Hz}$

Frequency is cycles per second; direction changes twice per cycle, so 100 times per second at 50 Hz.

Advantage of AC over DC

AC can be transmitted over long distances without much loss of energy

The one advantage named in the syllabus; write it as one clear sentence.

Wire colour code

$Live:red;neutral:black;earth:green$

Asked in true/false, MCQ and labelling questions.

Circuit ratings

15 A circuit: geysers, air coolers; 5 A circuit: bulbs, fans

Match appliances to circuits after finding current with $I=\frac{P}{V}$.

Short-circuit and overloading

Short-circuit	live touches neutral, current rises abruptly
Overloading	too much current
Overloading causes	a short-circuit, a voltage hike or too many appliances on one socket

State the cause clearly; the fuse melts by Joule heating in both cases.

Magnetic Effects of Electric Current: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the board asks Magnetic Effects of Electric Current

The question patterns to expect, and the method that works for each.

Tricks to remember Magnetic Effects of Electric Current

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Fleming's left-hand: FBI

  Thumb = F (Force), Forefinger = B (field), middle finger = I (current). Read the fingers from the thumb: F, B, I.

  Use it when: Any question on the direction of force or deflection of a beam in a magnetic field.

• Right for field, Left for force

  A current makes a field: Right hand. A field pushes a current: Left hand. 'Right makes, Left moves.'

  Use it when: Stops you picking the wrong hand under exam pressure.

• Electron flip

  Electron? Flip the arrow first. Current always runs opposite to electron motion; protons and alpha particles need no flip.

  Use it when: Beam deflection MCQs and the electron-in-a-field type question.

• Wire colours: Red Risky, Black Back, Green Ground

  Red live wire is the risky one, black neutral carries current back, green earth goes to the ground.

  Use it when: True/false, MCQ and labelling questions on domestic wiring.

• Clock face for solenoid poles

  Look at the end: current Anticlockwise means North (lines come Out to you); Clockwise means South.

  Use it when: Naming the poles of a solenoid or electromagnet from the current direction.

• 50 Hz, 100 flips

  Double the frequency to get the number of direction changes in one second.

  Use it when: Any question asking how often AC changes direction.

Magnetic Effects of Electric Current: board-level solved questions

Ordered from board level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section E style)

Read the situation, then answer every part. In the board paper this is a 4-mark question split into 1 + 1 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Magnetic Effects of Electric Current

The slips examiners see most often, and what to write instead.

• ✗Mistake: Reversing the direction of field lines inside a bar magnet

  Students remember 'N to S' and apply it everywhere, forgetting the lines must close.

  Wrong working

  Field lines go from north pole to south pole both outside and inside the magnet.

  Right working

  Outside the magnet the lines go from N to S; inside they go from S to N, so each line is a closed curve.

  ✓Do this: Always say 'outside' and 'inside' separately, and add 'closed curves' as the reason.

  Usually costs: 1 mark in MCQ or AR; ½ mark in a properties list.

• ✗Mistake: Using the wrong hand or wrong fingers for Fleming's rule

  The two rules are learned together and get mixed, especially the middle finger and forefinger.

  Wrong working

  Using the right hand: forefinger along current, middle finger along field, thumb gives force.

  Right working

  Left hand: forefinger along field, middle finger along current, thumb gives force; all three mutually perpendicular.

  ✓Do this: Learn FBI with the left hand and say the finger assignment aloud each time you practise.

  Usually costs: The full 1 to 2 marks for the direction; the final answer is wrong.

• ✗Mistake: Forgetting to flip the current for an electron beam

  Students treat the direction of motion of any particle as the current direction.

  Wrong working

  Electrons move east, so current is east; field downwards gives force towards the north.

  Right working

  Electrons move east, so current is west; field downwards gives force towards the south.

  ✓Do this: Write 'current is opposite to electron motion' as your first line before using the rule.

  Usually costs: 1 mark (wrong MCQ option) or the whole direction part of a longer answer.

• ✗Mistake: Saying the force reverses when both current and field are reversed

  Students remember 'reversing reverses' without checking how many quantities change.

  Wrong working

  If both the current and the magnetic field are reversed, the force on the conductor also reverses.

  Right working

  Reversing one reverses the force; reversing both brings it back, so the force direction stays the same.

  ✓Do this: Count the reversals: one reversal flips the force, two reversals cancel out.

  Usually costs: 1 mark in an assertion-reason question.

• ✗Mistake: Vague or wrong answer on the earth wire

  Students write that the earth wire 'stops short-circuits' or 'carries the current' without the mechanism.

  Wrong working

  The earth wire prevents short-circuits and saves the appliance.

  Right working

  The earth wire gives leaked current a low-resistance path and keeps the metal body at earth's potential, so the user does not get a severe shock. The fuse protects against short-circuits.

  ✓Do this: Use three key phrases: metallic body, low-resistance path, earth's potential and no severe shock.

  Usually costs: 1 to 2 marks in a 2- or 3-mark reasoning question.

• ✗Mistake: Mixing up short-circuiting and overloading

  Both cause a large current and the fuse melts in both, so students treat them as the same.

  Wrong working

  Short-circuit is when too many appliances are connected to one socket.

  Right working

  Short-circuit: the live and neutral wires touch directly, so current rises abruptly. Overloading is any excessive current, caused by a short-circuit, a voltage hike or too many appliances on one socket.

  ✓Do this: Define short-circuit by its cause (live touches neutral) and list the three causes of overloading.

  Usually costs: 1 mark per definition.

• ✗Mistake: Weak field-line diagram for a straight wire

  Students draw evenly spaced circles with no arrows and do not mark the current.

  Wrong working

  Three equally spaced circles around a dot, no arrows, no current direction shown.

  Right working

  Concentric circles centred on the wire, spaced farther apart moving outwards, arrows anticlockwise (seen from above) for current upwards, with the current direction marked and the right-hand thumb rule stated.

  ✓Do this: Draw and label checklist: wire, current arrow, at least three circles widening outwards, arrows on every circle, rule named.

  Usually costs: 1 to 1½ marks in a 3-mark diagram question.

NCERT exercise guide: Magnetic Effects of Electric Current

What each exercise in the NCERT chapter tests, how to approach it, and a question of the same kind solved step by step. Questions here are written in our own words.

Magnetic Effects of Electric Current: previous year questions

• Asked in 21 of the 21 board papers we hold (2023 to 2026), on average 5.1 marks per paper; 61 questions in all, counting OR alternatives. In 4 of 4 sample papers.

Counted from the real papers on our previous year papers page, not estimated. Average marks are over every board paper we hold, with an OR pair counted once. Chapter tags are ours.

Solved board questions from Magnetic Effects of Electric Current

Real questions from recent papers. Try each one first, then open our step-by-step solution with marks per step.

Every Magnetic Effects of Electric Current question, by year

Practice questions on Magnetic Effects of Electric Current

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQHOTS / competency

   In Activity 12.7, with current from B to A and the north pole of the magnet below the rod, the rod moves a small distance to the left. The student now reverses the current, interchanges the poles of the magnet, and also increases the current using the rheostat. What will be observed?
   (a) the rod moves to the left, through a larger distance
   (b) the rod moves to the right, through a larger distance
   (c) the rod moves to the left, through the same distance
   (d) the rod moves to the right, through the same distance

   Hint

   Count the reversals first, then think about the size of the force.

   Answer

   (a) the rod moves to the left, through a larger distance. Two reversals cancel, so the direction is unchanged, and a larger current gives a larger force.

2. Q2 · 3 marks · Short answerHarder board level

   Compare the magnetic field lines of a bar magnet with those around a straight current-carrying wire passing vertically through a horizontal sheet. Give two differences, and draw a labelled sketch of each pattern. (3 marks)

   Hint

   Think about shape, where the lines are crowded, and how the direction is found.

   Answer

   Differences:

   • Bar magnet: closed curves that leave the N pole and enter the S pole, going S to N inside. Wire: concentric circles centred on the wire, with no poles.
   • Bar magnet: lines most crowded near the poles. Wire: lines most crowded close to the wire and spread out away from it; direction given by the right-hand thumb rule.

   Draw and label (bar magnet): a rectangle marked N and S, closed curves from N round to S, crowded near the poles, arrows N to S outside and S to N inside, no lines crossing.

   Draw and label (wire): a dot or cross for the wire with the current direction marked, at least three concentric circles with gaps growing outwards, arrows on every circle matching the right-hand thumb rule.

3. Q3 · 1 mark · Assertion-reasonBoard level

   Assertion (A): A small compass moved along the axis inside a long current-carrying solenoid points in the same direction at every position.
   Reason (R): The field lines inside a long current-carrying solenoid are parallel straight lines.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

   Hint

   What does a set of parallel straight lines tell you about the field?

   Answer

   (a) Both are true and R explains A: parallel straight lines mean a uniform field, with the same direction at every point inside, so the compass points the same way everywhere.

4. Q4 · 3 marks · Short answerHarder board level

   A straight vertical wire passes through a horizontal cardboard and carries current downward.

   (a) In which direction does a compass needle point when placed due north of the wire? And due south of it?
   (b) What happens to the deflection if the compass is moved farther from the wire, current unchanged? (3 marks)

   Hint

   Thumb down: are the fingers clockwise or anticlockwise seen from above?

   Answer

   Right thumb down gives clockwise field lines seen from above.
   (a) North of the wire, clockwise motion is towards the east, so the needle points east; south of the wire it points west.
   (b) The deflection decreases because the field becomes weaker with distance from the wire.

5. Q5 · 3 marks · Short answerHarder board level

   An electric oven rated 1540 W is to be used in a house with a 5 A circuit and a 15 A circuit at 220 V.

   (a) Find the current it draws.
   (b) What happens if it is used on the 5 A circuit?
   (c) If it is used on the 15 A circuit, what is the largest extra power that can be added to that circuit at the same time? (3 marks)

   Hint

   Use I = P/V, then find the spare current.

   Answer

   (a) $I=\frac{1540}{220}=7$ A.
   (b) 7 A exceeds 5 A, so the fuse melts due to overloading and the oven stops.
   (c) Spare current = $15-7=8$ A; extra power = $220\times 8=1760$ W.

6. Q6 · 5 marks · Long answerHarder board level

   Describe how electricity reaches and is distributed in a house. Your answer should include the colour codes and potential difference of the wires, the two separate circuits, why appliances are in parallel, the role of the earth wire, and the role of the fuse in short-circuiting and overloading. (5 marks)

   Hint

   Follow the path: mains, fuse, meter, main switch, circuits, appliances.

   Answer

   Mains has a live wire (red) and a neutral wire (black) with 220 V between them; they pass through a main fuse into the meter and then a main switch. Separate circuits run from there: 15 A for high-power appliances such as geysers and 5 A for bulbs and fans. Appliances are in parallel so each gets the same 220 V and has its own switch. The green earth wire joins metal bodies to a plate deep in the earth, giving a low-resistance path so leaked current does not give a severe shock. The fuse melts by Joule heating when current rises too high, in a short-circuit (live touches neutral) or overloading (too many appliances, voltage rise).

7. Q7 · 3 marks · Short answerHarder board level

   A circular coil lies flat on a table and current flows through it clockwise when seen from above.

   (a) What is the direction of the field inside and outside the coil?
   (b) The coil is replaced by one of 20 turns carrying the same current. How does the field at the centre change, and why? (3 marks)

   Hint

   Apply the thumb rule to one side of the coil and look at the centre.

   Answer

   (a) Inside the coil the field points vertically downward into the table; outside, it points upward.
   (b) The field at the centre becomes 20 times as large, because the current in every turn is in the same direction and the field of each turn adds up.

8. Q8 · 3 marks · Short answerBoard level

   (a) Name the kind of current given by a cell and the kind supplied to homes.
   (b) Domestic supply is 220 V at 50 Hz. What does 50 Hz describe?
   (c) State one advantage of AC over DC. (3 marks)

   Hint

   One kind flows one way only; the other reverses again and again.

   Answer

   (a) A cell gives direct current (one direction only); homes get alternating current, which changes direction periodically.
   (b) 50 Hz is the frequency of AC: it completes 50 cycles every second, changing direction 100 times.
   (c) AC can be transmitted over long distances without much loss of energy.

9. Q9 · 3 marks · Short answerBoard level

   A student wrote these notes. Find the errors and correct them:
   (i) Inside a bar magnet, field lines run from the north pole to the south pole.
   (ii) The field of a bar magnet is strongest at its middle.
   (iii) The wire with green insulation is the live wire.
   (iv) Household appliances are connected in series so that each gets the same current. (3 marks)

   Hint

   Check each against direction, field strength, colour code and type of connection.

   Answer

   (i) Wrong: inside, lines run from S to N, making closed curves.
   (ii) Wrong: the field is strongest near the poles, where lines are crowded.
   (iii) Wrong: red is live, black is neutral, green is earth.
   (iv) Wrong: appliances are in parallel so each gets the same potential difference of 220 V.

10. Q10 · 2 marks · Short answerHOTS / competency

    A positively charged particle moves vertically downward and is deflected towards the east by a magnetic field. Find the direction of the field. If an electron moved vertically downward through the same field, which way would it be deflected? (2 marks)

    Hint

    For a positive charge, current is along its motion; for an electron, opposite.

    Answer

    Current downward (middle finger), force east (thumb): the forefinger points north, so the field is towards north.
    For an electron moving down, the current is upward, so the force reverses: it is deflected towards the west.

11. Q11 · 3 marks · Short answerHOTS / competency

    A 15 A circuit at 220 V supplies a geyser of 1980 W, an electric iron of 1320 W and a room heater of 1100 W, all switched on together.

    (a) Find the total current drawn and say what will happen.
    (b) The family must keep the geyser on. Which one other appliance should they switch off so that the circuit runs safely below its rating? Justify your choice with calculations. (3 marks)

    Hint

    Find each current with I = P/V, then test each choice against 15 A.

    Answer

    (a) Geyser: $\frac{1980}{220}=9$ A; iron: $\frac{1320}{220}=6$ A; heater: $\frac{1100}{220}=5$ A. Total $=20$ A, more than 15 A, so the circuit is overloaded and the fuse melts.
    (b) Switching off the heater leaves $9+6=15$ A, right at the rating with no margin. Switching off the iron leaves $9+5=14$ A, which is below 15 A. So switch off the iron.

12. Q12 · 4 marks · Case-basedHOTS / competency

    Read the passage and answer the questions.

    Suppose a student fixes a bar magnet on a sheet of white paper on a drawing board and plots its field lines with a small compass. She marks the two ends of the needle, moves the compass so its south end sits on the mark left by its north end, and repeats until she reaches the other pole. She notices that the needle deflects more as she nears either end of the magnet. In her final drawing, two of her lines cross each other near the north pole.

    (A) Why does the needle deflect more near the ends of the magnet? (1 mark)
    (B) In which direction do the field lines run inside the magnet, and why must this be so? (1 mark)
    (C) What is wrong with the two crossing lines, and how should she correct her drawing? (2 marks)
    OR
    (D) If she replaced the bar magnet with a current-carrying solenoid of the same size, how would her pattern compare, and what would the lines inside the solenoid look like? (2 marks)

    Hint

    Link each part to one property of field lines.

    Answer

    (A) The lines are crowded near the poles, so the field, and the force on the needle, is strongest there.
    (B) From the south pole to the north pole, because outside they run N to S and every field line must be a closed curve.
    (C) Field lines can never cross: at the crossing the needle would have to point two ways at once, which is impossible. She has made a plotting error and should re-plot those lines step by step so that they run side by side without touching.
    (D) Outside, the pattern would look like that of the bar magnet, with one end acting as N and the other as S. Inside the solenoid the lines would be parallel straight lines, showing a uniform field.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.What is the direction of field lines inside a bar magnet?Show answer

   From the south pole to the north pole.

2. 2.Why do two magnetic field lines never cross?Show answer

   At the crossing the compass would point in two directions at once, which is impossible.

3. 3.What shape are the field lines around a straight current-carrying wire?Show answer

   Concentric circles centred on the wire.

4. 4.What does the field inside a long current-carrying solenoid look like?Show answer

   Parallel straight lines: the field is uniform, the same at all points.

5. 5.When is the force on a current-carrying conductor in a magnetic field largest?Show answer

   When the current is at right angles to the magnetic field.

6. 6.In Fleming's left-hand rule, what does the middle finger show?Show answer

   The direction of current.

7. 7.What are the voltage and frequency of domestic AC supply in India?Show answer

   220 V and 50 Hz.

8. 8.What colour is the insulation of the live, neutral and earth wires?Show answer

   Live: red; neutral: black; earth: green.

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Can you state three properties of magnetic field lines and give the reason they never cross?
• ☐Can you draw the field lines of a bar magnet with arrows, showing the direction inside the magnet too?
• ☐Can you state the right-hand thumb rule and use it for a vertical wire carrying current upwards, seen from above?
• ☐Can you say how the field at a point near a straight wire changes with current and with distance?
• ☐Can you explain why the field at the centre of a loop is strong, and why a coil of n turns gives n times the field?
• ☐Can you name the pole at an end of a solenoid from the current direction, and say what the field inside is like?
• ☐Can you explain how an electromagnet is made and give two ways to make it stronger?
• ☐Can you state Fleming's left-hand rule and find the deflection of an electron beam in a given field?
• ☐Can you explain what 50 Hz means, how often AC changes direction and one advantage of AC over DC?
• ☐Can you decide the right circuit for an appliance using $I=\frac{P}{V}$ and explain the earth wire, fuse, short-circuit and overloading?

Magnetic Effects of Electric Current: frequently asked questions